1. Field of the Invention
The present invention relates to a light probe microscope for observing the shape of a sample surface and observing optical information of the sample surface by utilizing a force acting between a probe and a sample, or the like.
2. Description of the Related Art
A proximity field optical microscope (light probe microscope) utilizing a proximity field light emitted from the microscopic optical aperture of a probe tip or a scattered light at a sharp tip is a known device that is capable of performing optical observation with a high resolving power exceeding a restriction of the wavelength of light. By using the light probe microscope, it is possible to observe an optical picture with a resolving power exceeding an optical image which has been measured by using a conventional optical microscope and a highly sensitized camera and, at the same time, a surface shape can be observed as well.
In the light probe microscope, it is necessary to detect a weak light such as scattered light and fluorescent light radiated from the sample surface adjoining the light field locally existing at the probe tip. However, in the conventional light probe microscope, there are used a photomultiplier and an avalanche photodiode as a light detector.
Since a feeble light is detected in the light probe microscope, stray light is picked up in the photomultiplier whose light-intercepting face is large, so that noise becomes high. For example, where light from a probe having an optical aperture of 100 nm is converged by an objective lens having a magnification of 100 times, a size corresponding to the aperture becomes 10 μm in a primary picture. In contrast to this, a size of the light-intercepting face of the photomultiplier is several mm to several tens of mm, so that a major region does not contribute to detection, reacts with the stray light, and becomes a source of a dark count noise. In order to eliminate the stray light, it has been considered to insert a pin hole to an image formation face, but it is a very difficult operation to align an optical axis of the feeble light therewith. On the other hand, in the avalanche photodiode, the light-intercepting face is as relatively small as about 200 to 500 μm, so that it is not easily influenced by the stray light. However, also in this case, it is necessary to align the optical axis, so that a measuring operation becomes complex.